Under the order, two qualified railroad employees are required to operate trains where major speed restrictions are in place until the signal system is updated.

“Safety is our highest priority, and we must do everything we can to learn from this tragic crash and prevent future derailments,” U.S. Transportation Secretary Anthony Foxx said in a release.

The emergency order is to help ensure other Metro-North trains travel at safe speeds while the investigation is underway into the Dec. 1 crash that killed four and injured dozens. The train was travelling at 82 miles per hour in a 30 mph zone.

Additionally, the railroad must submit a plan for approval regarding passenger and employee safety by the end of December.

The Federal Railroad Administration also increased regulations following a crash in May 2013.

It will be months before an official cause is released regarding the latest incident in the Bronx, N.Y., but in a letter to Metropolitan Transit Authority Chairman and CEO, the state’s governor said, “the actions of engineer William Rockefeller were the initiating cause of this tragic accident.”